In the field of semiconductor devices exemplified by large scale integration circuits (hereinafter, LSI circuits), further development of microfine circuits and multilayer interconnection structures has ever been demanded in pursuit of higher integration and higher speed. Chemical mechanical polishing (hereinafter, CMP) is an enabling technology that has been used to achieve the purpose. CMP is a planarization process applied to a thin insulating film (e.g., SiO2 film) or a thin wiring metal film to smooth a substrate or to remove an unwanted thin metal film to leave a wiring pattern as disclosed, e.g., in U.S. Pat. No. 4,944,836.
A metal polishing slurry used for CMP generally contains abrasive grains (e.g., alumina) and an oxidizing agent (e.g., hydrogen peroxide) The fundamental mechanism of CMP is considered to be that the oxidizing agent oxidizes the surface of metal to form an oxide film, which is removed by the abrasive grains as reported in Journal of Electrochemical Society, 1991, vol. 138, No. 11, pp 3460-3464.
However, CMP using such a polishing slurry containing solid abrasive grains can cause defects, such as scratches, thinning (excessive polishing all over the polished surface), dishing (thinning of the polished metal surface into a cavity), and erosion (excessive polishing of the dielectric between metal wires and dishing of the metal wires),
CMP is usually followed by a cleaning step in which the polishing slurry remaining on the semiconductor is removed. The existence of the abrasive grains makes the post-CMP cleaning step complicated. Additionally, before the washing is disposed of as waste liquid, the solid grains should be separated by, for example, settlement, which incurs extra cost.
One of solutions to the problems is to use an abrasive-free polishing solution. Journal of Electrochemical Society, 2000, vol. 147, No. 10 pp 3907-3913 reports a metal polishing process using an abrasive-free polishing solution combined with a dry etching process. JP-A-2001-127019 discloses a metal polishing solution comprising hydrogen peroxide, malic acid, benzotriazole, ammonium polyacrylate, and water. According to these abrasiveless techniques, the projections of the metal film are selectively polished away while the depressions remaining filled with the metal film to provide a desired conductor pattern. Scratching is reduced because the friction with a polishing pad is far milder in the abrasiveless CMP than in the CHP using an abrasive-containing slurry.
Tungsten and aluminum have generally been used as wiring metals for interconnection structures. In pursuance of further heightened performance, LSI circuits using copper less resistant than tungsten or aluminum as a wiring metal have been developed. Among known copper wiring techniques is a damascene CMP process as taught, e.g., in JP-A-2-278822. A dual damascene process, in which trenches and vias are formed in an interlayer insulating film, and a wiring metal is deposited to simultaneously fill the trenches and the vias, has come into wide use. Copper of five or more nines purity has been used as a target material of copper deposition. The tendency toward a still finer wiring pattern for higher density has boosted the demand for improvements on conductivity and electron characteristics of copper wires. To meet the demand, use of a copper alloy, i.e., high-purity copper doped with a third component has recently started to be studied. It has also been demanded to develop a high-speed metal polishing technique enabling high productivity and high precision without contaminating the high purity material.
A wafer size has been increasing to improve productivity in the fabrication of LSI circuits. Wafers of 200 mm or larger in diameter are now widely used, and manufacture of LSI circuits from 300 mm or larger wafers has been launched. Because the difference in polishing rate between the central and the peripheral portions of a wafer increases with a wafer size, there has been a keen demand for improved uniformity of planarization across a wafer.
JP-A-49-122432 proposes a method of chemically polishing copper or a copper alloy without using a mechanical polishing means. However, chemical polishing merely relying on dissolving action has planarity problems such as dishing more than CMP in which projections of the metal are selectively removed both chemically and mechanically.
JP-A-2001-279231 discloses an aqueous dispersion for CMP which can suppress deterioration of a polishing pad. The proposed technique is to reduce the level difference of the surface to be polished.
JP-T-2002-538284 (WO/0053691) discloses a working composition containing a chelating agent selected from iminodiacetic acid and its salts, which is used to modify the surface of wafers. JP-A-2003-507694 discloses a CMP composition containing an α-amino acid.
A polishing composition for Cu damascene CMP is required to have selectivity to copper over tantalum (hereinafter referred to as Cu/Ta selectivity),